Flow Rate Calculator

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Estimate the volumetric flow rate of water by adjusting pipe length, pressure, and diameter.

INDICATIVE ESTIMATOR ONLY This tool provides theoretical estimates for general information. All plumbing design, pipe sizing, and hydraulic calculations must be performed by a licensed plumber in accordance with AS/NZS 3500.
Use the internal diameter (ID), not outside diameter (OD).
Standard mains pressure is typically 350-500 kPa.
*Enter valid positive numbers for calculation.
Estimated Flow Rate
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Litres/min

View how flow changes with different variables:

Length (m) Flow (L/min) Pressure (kPa) ID (mm)

Understanding Water Flow Rates

In plumbing, the flow rate determines how much water reaches your taps, showers, or appliances. Proper pipe sizing ensures that your system delivers adequate water volume without excessive noise or pressure loss.

How to Use This Estimator

Enter the details of your piping run to see a theoretical flow rate in Litres per minute (L/min):

  • Internal Pipe Diameter (ID): The measurement inside the pipe wall (not the outside). Common copper pipe sizes are DN15 (12.7mm ID), DN20 (19mm ID), etc.
  • Pressure (kPa): The available pressure at the start of the run. Standard Australian residential static pressure is usually limited to 500 kPa.
  • Length: The total length of the pipe run in metres.

Australian Plumbing Standards (AS/NZS 3500)

While this calculator helps visualize the relationship between pressure, diameter, and length, real-world plumbing requires strict adherence to AS/NZS 3500. Professional calculations must account for:

  • Friction Loss: Different materials (Copper, PEX, PVC) create different amounts of drag.
  • Head Loss: Vertical rise reduces pressure (approx 10 kPa loss per 1 metre rise).
  • Velocity Limits: Water velocity should generally not exceed 3.0 m/s to prevent water hammer and pipe erosion.
  • Fittings: Elbows and tees add significant "equivalent length" to the friction calculation.
Important Disclaimer

The results generated by this tool are for illustrative purposes only and do not constitute professional engineering or plumbing advice. GPS Gas Plumbing Services accepts no liability for errors or omissions. For accurate sizing compliant with Australian Standards, always consult a licensed plumber.

Need accurate pipe sizing for your project? Contact GPS Gas Plumbing Services for professional advice in Sydney.